Process of rust proofing and articles produced thereby



?atented Aug. 23, 1927.

UNITED STATES PATENT OFFICE.

MATTHEW GREEN, 0F DETROITL AND HOBART H. WILLARD, OF A NN' ARBOR, MICHI-GAN, ASSIGNORS TO PARKER.RUST-PROOF COMPANY, 01 DETROIT, MICHIGAN, A,

CORPORATION OF MICHIGAN.

PROCESS OF RUST P ROOFING AND ARTICLES PRODUCED THEBEBY.

No Drawing. Application filed May 1b,

This invention relatesto a process of rustprooting iron articles and tothe articles rustproofcd in this manner.

More particularly, the invention relates to producing on the surface ofiron articles a coating of phosphates which are insoluble in Water, andto the articles coated in this manner.

The process of rust-proofing iron articles by producing thereon acoating of insoluble phosphates is well-known. While other materialshave been used to some extent, the coatings Which have been producedhave been essentially phosphates of iron. Analysis shows that, Whileother phosphates are present to some extent, .the major portion of thecoating consists of ferrous monohydrogen phosphate. This particularphosphate is slightly soluble and, therefore, does not furnish completeprotection against rusting.

it has been discovered that, when mangunese dihydrogen phosphateis'present in the rust-proofing bath in considerable proportionsrelatively to the other materials in the bath, aconsiderable portion ofthe coating consists of phosphate of manganese. The exact composition ofthe different phosphates in such a coating is very difiicult todetermine, but it has been discovered that, when a considerablepercentage of manganese is present in such a coating, the proportion ofphosphorus to metal in the coating more nearly approaches that presentin r the normal phosphate than thatpresent in the monohydro'genphosphate. The exact proportion may be varied by many conditions, butthe following examples may be mentioned in order to bring out clearlythe intended distinction. When the coating contains iron and manganeseatoms in about the ratio of two to one, the ratio of the metal tophosphorus is a trifle greater than that which would result from thecoating being one-half monohydrogen phosphate and one-half nor- Withmanganese forming about one-half of the metal in the coating, theproportion of metal in the coatingto phosphorus in the coating was foundto mdicate a proportion of approximately 6/? normal phosphate and 1/7monohydrogen phosphate. In the monohydrogenphosphate these atoms ofmetal and phosphorus are in 1926. semi No. 108,162.

the ratio of 1 to 1, while in the normal phosphate the ratio is 3 to 2.Analyses of coatings containing-iron and manganese in the proportion of2 to l have shown an atomic proportion .of 5 to 4 of metal tophosphorus, and similarly a proportion of 1 to 1 in the metals has showna proportion of 1.4+ to 1 of metal to phosphorus.

Normal phosphate is much less soluble than monohydrogen phosphate, andcorrosion tests corroborate the analyses described above. That is,coatings comparatively high in manganese and apparently high in normalphosphate are found to be much more resistant to rusting than coatings.consisting largely of monohydrogen phosphate.

' While this eflect is gradually increased with the increase ofmanganese in the coating, it appears that the proportion of normalphosphate is increased more rapidly than the proportion of manganese,and that a proportion of manganese amounting to onehalf as'much as theiron in the coating is decidedly effective in increasing the quality ofthe coating, but that a percentage of manganese equaling that of theiron in the coating produces a very much more resistant coating. WVhilebeneficial results may be obtained from our invention by having presentin the coating an amount of manganese equal to one-half ofthe iron inthe coating, it is preferable to have at least as much manganese as ironin the coating in order to obtain a protective layer which issubstantially normal phosphate.

'It has been found that, where manganese dihydrogen phosphate andferrous dillydrogen phosphate are present in a rustproofing solution,the manganese phosphate being less than the ferrous phosphate, there isa selective action Which'results in producing in the coating a largerproportion of manganese than there is in solution in the bath. Forexample, one-third as much manga'nese. as iron in a bath may result inonehalf as much manganese as iron in the coating, while approximatelyone-half as' much manganese as iron in the bath will produceapproximately as much manganese as iron inthe coating. It will beunderstood that many conditions alter these. proportions to some extent,and that the proportions given above are for purposes o illustration andare not. given as being fixed ratios under all circumstances.

. gen phosphate.

There are several ways in which a bath of the desired composition may beobtained.

Some of these ways will be described If manganous dihydrogenorthophosphate is dissolved in water, and the water boiled for sometime, a portion of the phosphate is precipitated as an insolublephosphate and some free acid is liberated. We have found that from sevento seventy pounds of the said phosphate dissolved in one hundredtwenty-five gallons of water and boiled as described will produce asatisfactory rustsludge, and

proofing solution, twenty to twenty-five pounds being the preferredamount. When an iron article, or an article havlng asurface containingiron, is immersed in such a solution, the formation of a, rust-proofingcoating begins at once. There is no preliminary pickling of the work tobring the solution into balance, such as necessarily results where freeacid is added to the bath and where iron must be dissolved from the workto bring the solution into balance, and the articles do not loseappreciably in weight or measurably in size. Nevertheless, in theprocess of forming the coating, a certain amount of the iron isdissolved in the bath. Some of this .is fixed as insoluble phosphates incoating, some of it forms insoluble phosphates which are deposited asart of it remains as ferrous dihydrogen p osphate dissolved in the bath.It will be readily understood that more of the phosphate radicals are incombination with a given amount of manganese in the dihydrogen phosphatethan there are in the insoluble coating and, therefore, the phosphateintroduced into the bath introduces sufficient phosphate radicals toform the phosphates of iron mentioned above.

If the bath is used continuously for rustproofing purposes for aconsiderable time, it constantly becomes less rich in manganese andricher in iron, reference being had to these materials dissolved in thebath in the form of dihydrogen phosphate. When the bath is replenishedby an additional amount of manganese phosphate, the proportion ofmanganese to 1ron is increased, but is not brought back to theproportion which it had originally. The proportion of iron in the bathcontinues'to increase until it reaches a certain percentage inproportion to the maximum acidity. Thereafter the iron in the bath seemsto remain approximately constant, whereas the manganese and acid areincreased when constant iron content is replenished with manganesephosphate, it maybe easily brought up to a point where the manganese 4will be more than half as much as the iron in the bath, but as this bathis used for" rust-proofing purposes the manganesemay be almostcompletely exhausted from the bath before the deposition of acoatingwill cease. In such a case, the'coating last formed isprincipally ferrous monohydrogen phosphate. By replenishing atcomparatively short intervals, the amount of.

manganese in the bath may be kept above one-third as much as the iron,with a result of producing more normal phosphate than monohydrogenphosphate in the coating. The strength of the rust-proofing solution maybe varied considerably and still rustproofeffectively. However, as theamount of iron in the bath seems to be approximately relative to themaximum acidity of the bath, it is preferable to replenish the bath tobring it each time to approximately the same strength. In this way theproportion of'manganese to iron is increased to the highest practicableamount at. each replenishment.

Theoretically, the best results would be obtained by replenishing thebath constantly so as to keep itat a substantially constant strength, asthat would maintain the proportion of manganese in thebath at itshighest point continuously. However, there are some objections toreplenishing during the time of rust-proofing in the same bath, and thenext best results are obtained by replenishing after each load. As it isdesirable to allow some time for the bath to, become uniform after eachreplenishment,- there is some delay due to replenishing after each load.Satisfactory results may be ob,- ta'ined by replenishing after everyother load. In general, it may be stated that the manner and frequencyof replenishment will depend to some extent upon the quality of thecoating desired. For the highest quality of coating, the bath should bekept as nearly as is practicable to the highest available proportion ofmanganese. Sometimes the coating produced with a less percentage ofmanganese is entirely suflicient for the desired purposes, and in suchcases less care is required in maintaining the bath with a uniformlyhigh manganese content.

III

While the preferred method of replenishing the bath is by adding amaterial consisting essentially of manganese dihydrogen phosphate, itwill be understood that other methods may be used for obtaining thedesired bath. This invention relates more especially to. the bath whichis desired, to the manner of replenishment, and to the coating produced.Various modifications may be made within the scope of the appendedclaims. 1

What we claim is:

1. Iron or steel or articles com osed or having asurface of iron orsteel urnished with a coating or deposit of hosphates of iron and ofmanganese, there eing at least one-half as much manganese as iron in thecoating.

2. Iron or steel or articles com osed or having a surface of iron orsteel rnished with a coating or deposit of phosphates of iron and ofmanganese, there being in the coating more than six atoms of the metalto five atoms of phosphorus.

3. A method of rust-proofin articles of iron or having a surface of ironor steel which consists in forming a dilute solution of phosphoric acidand dihydrogen phosphates of iron and manganese, there being at leastone-third as much manganese as iron in the solution and there beingsufficient dihydrogen phosphates in the solution in proportion to thefree acid to rustroof articles without reducing the weight thereof,placing iron or steel articles in the solution and maintaining thesolution hot until {the articles are rust-proofed.

4. The method of rust-proofing articlesof iron or having a surface ofiron or steel which consists in forming a dilute solution of phosphoricacid and dihydrogen phosphates of iron and manganese, there being atleast one-third as much manganese as iron in the solution and therebeing sufiicient dihydrogen phosphates in the solution in proportion tothe free acid to rust-proof articles without reducing the weightthereof, placing iron or'steel articles in the solution and maintainingthe solution hot until the articles are rust-proofed, introducing otherarticles into the bath and repeating the process and adding tothesolution from time to time materials which maintain the amount ofmanganese in the solution above one-third the iron in the solution.

5. A solution for rust-proofing purposes containing dihydrogenphosphates of manganse and iron and free acid, the phosphates being insufiicient amounts so as to rustproof an immersed iron article withoutsignificant loss of-weight and the manganese in the dissolved phosphatesbeing more than one-third as much as the iron in the dissolvedphosphates.

In testimony whereof we have hereunto signed our names to thisspecification. HOBART H. WILLARD. MATTHEW GREEN.

